Inner gantry

ABSTRACT

A system includes a patient support and an outer gantry on which an accelerator is mounted to enable the accelerator to move through a range of positions around a patient on the patient support. The accelerator is configured to produce a proton or ion beam having an energy level sufficient to reach a target in the patient. An inner gantry includes an aperture for directing the proton or ion beam towards the target.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/221,855, filed Jul. 28, 2016; U.S. patent application Ser. No.15/221,855 being a continuation of U.S. patent application Ser. No.14/542,966, filed Nov. 17, 2014 and patented as U.S. Pat. No. 9,452,301on Sep. 27, 2016; U.S. patent application Ser. No. 14/542,966 being acontinuation of U.S. patent application Ser. No. 13/532,530, filed Jun.25, 2012 and patented as U.S. Pat. No. 8,916,843 on Dec. 23, 2014; U.S.patent application Ser. No. 13/532,530 being a continuation of U.S.patent application Ser. No. 12/275,103, filed Nov. 20, 2008 and patentedas U.S. Pat. No. 8,344,340 on Jan. 1, 2013; U.S. patent application Ser.No. 12/275,103 claiming the benefit of priority of U.S. ProvisionalApplication No. 60/991,454 filed on Nov. 30, 2007; U.S. patentapplication Ser. No. 12/275,103 being a continuation-in-part of U.S.patent application Ser. No. 11/601,056, filed on Nov. 17, 2006 andpatented as U.S. Pat. No. 7,728,311 on Jun. 1, 2010; U.S. patentapplication Ser. No. 11/601,056 claiming the benefit of priority of U.S.Provisional Application No. 60/738,404, filed on Nov. 18, 2005. Theforegoing applications to which this application claims priority, areincorporated by reference into this application, including: Ser. Nos.15/221,855; 14/542,966; 13/532,530; 12/275,103; 60/991,454; 11/601,056;and; 60/738,404.

TECHNICAL FIELD

This patent application describes an inner gantry for use with aparticle beam therapy system.

BACKGROUND

The design of a proton or ion radiation therapy system for a clinicalenvironment should take account of overall size, cost, and complexity.Available space is usually limited in crowded clinical environments.Lower cost allows more systems to be deployed to reach a broader patientpopulation. Less complexity reduces operating costs and makes the systemmore reliable for routine clinical use.

Other considerations may also bear on the design of such a therapysystem. By configuring the system to apply the treatment to patients whoare held in a stable, reproducible position (for example, lying supineon a flat table), the physician can more precisely relocate the intendedtarget, relative to the patient's anatomy, at each treatment. Reliablereproduction of the patient's position for each treatment also can beaided using custom molds and braces fitted to the patient. With apatient in a stable, fixed position, the radiotherapy beam can bedirected into the patient from a succession of angles, so that, over thecourse of the treatment, the radiation dose at the target is enhancedwhile the extraneous radiation dose is spread over non-target tissues.

Traditionally, an isocentric gantry is rotated around the supine patientto direct the radiation beam along successive paths that lie at a rangeof angles in a common vertical plane toward a single point (called anisocenter) within the patient. By rotating the table on which thepatient lies around a vertical axis, the beam can be directed into thepatient along different paths. Other techniques have been used to varythe position of the radiation source around the patient, includingrobotic manipulation.

SUMMARY

In general, this patent application describes a system comprising apatient support and an outer gantry on which an accelerator is mounted.The outer gantry enables the accelerator to move through a range ofpositions around a patient on the patient support. The accelerator isconfigured to produce a proton or ion beam having an energy levelsufficient to reach a target in the patient. An inner gantry comprisesan aperture for directing the proton or ion beam towards the target. Thesystem described above may include one or more of the followingfeatures, either alone or in combination.

The inner gantry may comprise an applicator for holding the aperture.The applicator may be movable along the inner gantry. The applicator maybe configured to move the aperture relative to the patient. For example,the applicator may be configured to move the aperture towards, or awayfrom, the patient.

The inner gantry may comprise a track along which the applicator isconfigured to move. A cover may be movable relative to the track. Thecover may be for preventing objects from falling into a vault below thepatient support.

A processing device may be programmed to control movement of the outergantry and/or the inner gantry. The processing device may be configuredto control movement of the outer gantry and/or the inner gantry tosubstantially align the proton or ion beam with the aperture. Theaperture may be configured to substantially collimate the proton or ionbeam. The system may comprise a patient support that is movable relativeto the inner gantry and/or the outer gantry.

In general, this patent application also describes a system comprising apatient support and a gantry on which a particle beam accelerator ismounted. The particle beam accelerator is for directing a particle beamtowards the patient support. The gantry is movable to positions aboveand below the patient support. An aperture is located between theparticle beam accelerator and the patient support. The aperture is formodifying the particle beam. The system described above may include oneor more of the following features, either alone or in combination.

The system may comprise an apparatus to hold the aperture. The apparatusmay be movable relative to the patient support. The apparatus maycomprise a robotic arm that is computer controlled to position theaperture relative to the patient support. The apparatus may comprise astand, which is manually positionable, to hold the aperture.

The particle beam accelerator may be a synchrocyclotron. The system maycomprise a second gantry that includes an applicator to hold theaperture. The second gantry may be controlled to substantially align theaperture with the particle beam.

In general, this patent application also describes a system comprising apatient support, a first gantry that is angularly movable relative tothe patient support, and a particle accelerator that is mounted on thefirst gantry. The particle accelerator is configured to provide aparticle beam directly towards the patient support. A second gantry ispositioned relative to the patient support. The second gantry issubstantially C-shaped. The system described above may include one ormore of the following features, either alone or in combination.

The second gantry may comprise a track, an aperture, and an applicator.The applicator may be movable along the track so that the aperture issubstantially aligned with the particle beam. The aperture may alter theparticle beam before the particle beam reaches a patient on the patientsupport.

The system may comprise a computer to control the first gantry and thesecond gantry. The first gantry may be movable so that the particleaccelerator is in a position above the patient support to a positionbelow the patient support. The second gantry may comprise a cover toprotect the particle accelerator when the particle accelerator is in theposition below the patient support. The inner gantry may comprise adevice to alter a size and/or shape of the particle beam. The device foraltering the particle beam may be movable relative to thesynchrocyclotron.

Any of the foregoing features may be combined to form implementationsnot specifically described herein.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Further features, aspects, andadvantages will become apparent from the description, the drawings, andthe claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a therapy system.

FIG. 2 is an exploded perspective view of components of asynchrocyclotron.

FIGS. 3, 4, and 5 are cross-sectional views of a synchrocyclotron.

FIG. 6 is a perspective view of a synchrocyclotron.

FIG. 7 is a cross-sectional view of a portion of a reverse bobbin andwindings.

FIG. 8 is a cross sectional view of a cable-in-channel compositeconductor.

FIG. 9 is a cross-sectional view of an ion source.

FIG. 10 is a perspective view of a dee plate and a dummy dee.

FIG. 11 is a perspective view of a vault.

FIG. 12 is a perspective view of a treatment room with a vault.

FIG. 13 shows a perspective view of a treatment room.

FIG. 14 shows a patient positioned within an inner gantry in a treatmentroom.

FIG. 15 is a perspective view showing both the outer and inner gantriespositioned to apply a proton or ion beam from above the patient.

FIG. 16 shows the shape of a particle beam provided by an accelerator.

FIG. 17 is a perspective view showing both the outer and inner gantriespositioned to apply a proton or ion beam from above below the patient.

FIG. 18 shows components of the inner gantry.

FIG. 19 shows a robotic arm used to perform functions of the innergantry.

DETAILED DESCRIPTION

As shown in FIG. 1, a charged particle radiation therapy system 500includes a beam-producing particle accelerator 502 having a weight andsize small enough to permit it to be mounted on a rotating gantry 504with its output directed straight (that is, essentially directly) fromthe accelerator housing toward a patient 506.

In some implementations, the steel gantry has two legs 508, 510 mountedfor rotation on two respective bearings 512, 514 that lie on oppositesides of the patient. The accelerator is supported by a steel truss 516that is long enough to span a treatment area 518 in which the patientlies (e.g., twice as long as a tall person, to permit the person to berotated fully within the space with any desired target area of thepatient remaining in the line of the beam) and is attached stably atboth ends to the rotating legs of the gantry.

In some examples, the rotation of the gantry is limited to a range 520of less than 360 degrees, e.g., about 180 degrees, to permit a floor 522to extend from a wall of the vault 524 that houses the therapy systeminto the patient treatment area. The limited rotation range of thegantry also reduces the required thickness of some of the walls (whichnever directly receive the beam, e.g., wall 530), which provideradiation shielding of people outside the treatment area. A range of 180degrees of gantry rotation is enough to cover all treatment approachangles, but providing a larger range of travel can be useful. Forexample the range of rotation may be between 180 and 330 degrees andstill provide clearance for the therapy floor space.

The horizontal rotational axis 532 of the gantry is located nominallyone meter above the floor where the patient and therapist interact withthe therapy system. This floor is positioned about 3 meters above thebottom floor of the therapy system shielded vault. The accelerator canswing under the raised floor for delivery of treatment beams from belowthe rotational axis. The patient couch moves and rotates in asubstantially horizontal plane parallel to the rotational axis of thegantry. The couch can rotate through a range 534 of about 270 degrees inthe horizontal plane with this configuration. This combination of gantryand patient rotational ranges and degrees of freedom allow the therapistto select virtually any approach angle for the beam. If needed, thepatient can be placed on the couch in the opposite orientation and thenall possible angles can be used.

In some implementations, the accelerator uses a synchrocyclotronconfiguration having a very high magnetic field superconductingelectromagnetic structure. Because the bend radius of a charged particleof a given kinetic energy is reduced in direct proportion to an increasein the magnetic field applied to it, the very high magnetic fieldsuperconducting magnetic structure permits the accelerator to be madesmaller and lighter. The synchrocyclotron uses a magnetic field that isuniform in rotation angle and falls off in strength with increasingradius. Such a field shape can be achieved regardless of the magnitudeof the magnetic field, so in theory there is no upper limit to themagnetic field strength (and therefore the resulting particle energy ata fixed radius) that can be used in a synchrocyclotron.

Certain superconducting materials begin to lose their superconductingproperties in the presence of very high magnetic fields. Highperformance superconducting wire windings are used to allow very highmagnetic fields to be achieved.

Superconducting materials typically need to be cooled to lowtemperatures for their superconducting properties to be realized. Insome examples described here, cryo-coolers are used to bring thesuperconducting coil windings to temperatures near absolute zero. Usingcryo-coolers can reduce complexity and cost.

The synchrocyclotron is supported on the gantry so that the beam isgenerated directly in line with the patient. The gantry permits rotationof the cyclotron about a horizontal rotational axis that contains apoint (isocenter 540) within, or near, the patient. The split truss thatis parallel to the rotational axis, supports the cyclotron on bothsides.

Because the rotational range of the gantry is limited, a patient supportarea can be accommodated in a wide area around the isocenter. Becausethe floor can be extended broadly around the isocenter, a patientsupport table can be positioned to move relative to and to rotate abouta vertical axis 542 through the isocenter so that, by a combination ofgantry rotation and table motion and rotation, any angle of beamdirection into any part of the patient can be achieved. The two gantryarms are separated by more than twice the height of a tall patient,allowing the couch with patient to rotate and translate in a horizontalplane above the raised floor.

Limiting the gantry rotation angle allows for a reduction in thethickness of at least one of the walls surrounding the treatment room.Thick walls, typically constructed of concrete, provide radiationprotection to individuals outside the treatment room. A wall downstreamof a stopping proton beam may be about twice as thick as a wall at theopposite end of the room to provide an equivalent level of protection.Limiting the range of gantry rotation enables the treatment room to besited below earth grade on three sides, while allowing an occupied areaadjacent to the thinnest wall reducing the cost of constructing thetreatment room.

In the example implementation shown in FIG. 1, the superconductingsynchrocyclotron 502 operates with a peak magnetic field in a pole gapof the synchrocyclotron of 8.8 Tesla. The synchrocyclotron produces abeam of protons having an energy of 250 MeV. In other implementationsthe field strength could be in the range of 6 to 20 Tesla and the protonenergy could be in the range of 150 to 300 MeV

The radiation therapy system described in this example is used forproton radiation therapy, but the same principles and details can beapplied in analogous systems for use in heavy ion (ion) treatmentsystems.

As shown in FIGS. 2, 3, 4, 5, and 6, an example synchrocyclotron 10 (502in FIG. 1) includes a magnet system 12 that contains an ion source 90, aradiofrequency drive system 91, and a beam extraction system 38. Themagnetic field established by the magnet system has a shape appropriateto maintain focus of a contained proton beam using a combination of asplit pair of annular superconducting coils 40, 42 and a pair of shapedferromagnetic (e.g., low carbon steel) pole faces 44, 46.

The two superconducting magnet coils are centered on a common axis 47and are spaced apart along the axis. As shown in FIGS. 7 and 8, thecoils are formed by of Nb3Sn-based superconducting 0.6 mm diameterstrands 48 (that initially comprise a niobium-tin core surrounded by acopper sheath) deployed in a Rutherford cable-in-channel conductorgeometry. After six individual strands are laid in a copper channel 50,they are heated to cause a reaction that forms the final (brittle)material of the winding. After the material has been reacted, the wiresare soldered into the copper channel (outer dimensions 3.02×1.96 mm andinner dimensions 2.05×1.27 mm) and covered with insulation 52 (in thisexample, a woven fiberglass material). The copper channel containing thewires 53 is then wound in a coil having a rectangular cross-section of6.0 cm×15.25 cm, having 30 layers and 47 turns per layer. The wound coilis then vacuum impregnated with an epoxy compound 54. The finished coilsare mounted on an annular stainless steel reverse bobbin 56. A heaterblanket 55 is held against the inner face of the bobbin and the windingsto protect the assembly in the event of a magnet quench. In an alternateversion, the superconducting coil may be formed of 0.8 mm diameter Nb3Snbased strands. These strands can be deployed in a 4 strand cable, heattreated to form the superconducting matrix and soldered into a copperchannel of outer dimension 3.19 by 2.57 mm. The integrated cable inchannel conductor can be insulated with overlapped woven fiberglass tapeand then wound into coils of 49 turns and 26 layers deep with arectangular cross section of 79.79 mm by 180.5 mm and inner radius of374.65 mm. The wound coil is then vacuum impregnated with an epoxycompound. The entire coil can then be covered with copper sheets toprovide thermal conductivity and mechanical stability and then containedin an additional layer of epoxy. The precompression of the coil can beprovided by heating the stainless steel reverse bobbin and fitting thecoils within the reverse bobbin. The reverse bobbin inner diameter ischosen so that when the entire mass is cooled to 4 K, the reverse bobbinstays in contact with the coil and provides some compression. Heatingthe stainless steel reverse bobbin to approximately 50 degrees C. andfitting coils at room temperature (20 degrees C.) can achieve this.

The geometry of the coil is maintained by mounting the coils in a“reverse” rectangular bobbin 56 and incorporating a pre-compressionstainless steel bladder 58 between each coil and an inner face 57 of thebobbin to exert a restorative force 60 that works against the distortingforce produced when the coils are energized. The bladder ispre-compressed after the coils and the heater blanket are assembled onthe bobbin, by injecting epoxy into the bladder and allowing it toharden. The precompression force of the bladder is set to minimize thestrain in the brittle Nb3Sn superconducting matrix through all phases ofcool-down and magnet energizing.

As shown in FIG. 5, the coil position is maintained relative to themagnet yoke and cryostat using a set of warm-to-cold support straps 402,404, 406. Supporting the cold mass with thin straps reduces the heatleakage imparted to the cold mass by the rigid support system. Thestraps are arranged to withstand the varying gravitational force on thecoil as the magnet rotates on board the gantry. They withstand thecombined effects of gravity and the large de-centering force realized bythe coil when it is perturbed from a perfectly symmetric positionrelative to the magnet yoke. Additionally the links act to reducedynamic forces imparted on the coil as the gantry accelerates anddecelerates when its position is changed. Each warm-to-cold supportincludes 3 S2 fiberglass links. Two links 410, 412 are supported acrosspins between the warm yoke and an intermediate temperature (50-70 K),and one link 408 is supported across the intermediate temperature pinand a pin attached to the cold mass. Each link is 10.2 cm long (pincenter to pin center) and is 20 mm wide. The link thickness is 1.59 mm.Each pin is made of stainless steel and is 47.7 mm in diameter.

Referring to FIG. 3, the field strength profile as a function of radiusis determined largely by choice of coil geometry; the pole faces 44, 46of the permeable yoke material can be contoured to fine tune the shapeof the magnetic field to ensure that the particle beam remains focusedduring acceleration.

The superconducting coils are maintained at temperatures near absolutezero (e.g., about 4 degrees Kelvin) by enclosing the coil assembly (thecoils and the bobbin) inside an evacuated annular aluminum or stainlesssteel cryostatic chamber 70 that provides a free space around the coilstructure, except at a limited set of support points 71, 73. In analternate version (FIG. 4) the outer wall of the cryostat may be made oflow carbon steel to provide an additional return flux path for themagnetic field. The temperature near absolute zero is achieved andmaintained using two Gifford-McMahon cryo-coolers 72, 74 that arearranged at different positions on the coil assembly. Each cryo-coolerhas a cold end 76 in contact with the coil assembly. The cryo-coolerheads 78 are supplied with compressed Helium from a compressor 80. Twoother Gifford-McMahon cryo-coolers 77, 79 are arranged to cool hightemperature (e.g., 60-80 degrees Kelvin) leads 81 that supply current tothe superconducting windings.

The coil assembly and cryostatic chambers are mounted within and fullyenclosed by two halves 81, 83 of a pillbox-shaped magnet yoke 82. Inthis example, the inner diameter of the coil assembly is about 140 cm.The iron yoke 82 provides a path for the return magnetic field flux 84and magnetically shields the volume 86 between the pole faces 44, 46 toprevent external magnetic influences from perturbing the shape of themagnetic field within that volume. The yoke also serves to decrease thestray magnetic field in the vicinity of the accelerator.

As shown in FIGS. 3 and 9, the synchrocyclotron includes an ion source90 of a Penning ion gauge geometry located near the geometric center 92of the magnet structure 82. The ion source may be as described below, orthe ion source may be of the type described in U.S. patent applicationSer. No. 11/948,662, entitled “Interrupted Particle Source”, thecontents of which are incorporated herein by reference as if set forthin full. Ion source 90 is fed from a supply 99 of hydrogen through a gasline 101 and tube 194 that delivers gaseous hydrogen. Electric cables 94carry an electric current from a current source 95 to stimulate electrondischarge from cathodes 192, 190 that are aligned with the magneticfield, 200.

In this example, the discharged electrons ionize the gas exiting througha small hole from tube 194 to create a supply of positive ions (protons)for acceleration by one semicircular (dee-shaped) radio-frequency plate100 that spans half of the space enclosed by the magnet structure andone dummy dee plate 102. In the case of an interrupted ion source, all(or a substantial part) of the tube containing plasma is removed at theacceleration region, thereby allowing ions to be more rapidlyaccelerated in a relatively high magnetic field.

As shown in FIG. 10, the dee plate 100 is a hollow metal structure thathas two semicircular surfaces 103, 105 that enclose a space 107 in whichthe protons are accelerated during half of their rotation around thespace enclosed by the magnet structure. A duct 109 opening into thespace 107 extends through the yoke to an external location from which avacuum pump 111 can be attached to evacuate the space 107 and the restof the space within a vacuum chamber 119 in which the acceleration takesplace. The dummy dee 102 comprises a rectangular metal ring that isspaced near to the exposed rim of the dee plate. The dummy dee isgrounded to the vacuum chamber and magnet yoke. The dee plate 100 isdriven by a radio-frequency signal that is applied at the end of aradio-frequency transmission line to impart an electric field in thespace 107. The radio frequency electric field is made to vary in time asthe accelerated particle beam increases in distance from the geometriccenter. Examples of radio frequency waveform generators that are usefulfor this purpose are described in U.S. patent application Ser. No.11/187,633, titled “A Programmable Radio Frequency Waveform Generatorfor a Synchrocyclotron,” filed Jul. 21, 2005, and in U.S. ProvisionalApplication No. 60/590,089, same title, filed on Jul. 21, 2004, both ofwhich are incorporated herein by reference as if set forth in full. Theradio frequency electric field may be controlled in the manner describedin U.S. patent application Ser. No. 11/948,359, entitled “Matching AResonant Frequency Of A Resonant Cavity To A Frequency Of An InputVoltage”, the contents of which are incorporated herein by reference asif set forth in full.

For the beam emerging from the centrally located ion source to clear theion source structure as it begins to spiral outward, a large voltagedifference is required across the radio frequency plates. 20,000 Voltsis applied across the radio frequency plates. In some versions from8,000 to 20,000 Volts may be applied across the radio frequency plates.To reduce the power required to drive this large voltage, the magnetstructure is arranged to reduce the capacitance between the radiofrequency plates and ground. This is done by forming holes withsufficient clearance from the radio frequency structures through theouter yoke and the cryostat housing and making sufficient space betweenthe magnet pole faces.

The high voltage alternating potential that drives the dee plate has afrequency that is swept downward during the accelerating cycle toaccount for the increasing relativistic mass of the protons and thedecreasing magnetic field. The dummy dee does not require a hollowsemi-cylindrical structure as it is at ground potential along with thevacuum chamber walls. Other plate arrangements could be used such asmore than one pair of accelerating electrodes driven with differentelectrical phases or multiples of the fundamental frequency. The RFstructure can be tuned to keep the Q high during the required frequencysweep by using, for example, a rotating capacitor having intermeshingrotating and stationary blades. During each meshing of the blades, thecapacitance increases, thus lowering the resonant frequency of the RFstructure. The blades can be shaped to create a precise frequency sweeprequired. A drive motor for the rotating condenser can be phase lockedto the RF generator for precise control. One bunch of particles isaccelerated during each meshing of the blades of the rotating condenser.

The vacuum chamber 119 in which the acceleration occurs is a generallycylindrical container that is thinner in the center and thicker at therim. The vacuum chamber encloses the RF plates and the ion source and isevacuated by the vacuum pump 111. Maintaining a high vacuum insures thataccelerating ions are not lost to collisions with gas molecules andenables the RF voltage to be kept at a higher level without arcing toground.

Protons traverse a generally spiral path beginning at the ion source. Inhalf of each loop of the spiral path, the protons gain energy as theypass through the RF electric field in space 107. As the ions gainenergy, the radius of the central orbit of each successive loop of theirspiral path is larger than the prior loop until the loop radius reachesthe maximum radius of the pole face. At that location a magnetic andelectric field perturbation directs ions into an area where the magneticfield rapidly decreases, and the ions depart the area of the highmagnetic field and are directed through an evacuated tube 38 to exit theyoke of the cyclotron. The ions exiting the cyclotron will tend todisperse as they enter the area of markedly decreased magnetic fieldthat exists in the room around the cyclotron. Beam shaping elements 107,109 in the extraction channel 38 redirect the ions so that they stay ina straight beam of limited spatial extent.

The magnetic field within the pole gap needs to have certain propertiesto maintain the beam within the evacuated chamber as it accelerates. Themagnetic field index n, which is shown below,n=−(r/B)dB/dr,should be kept positive to maintain this “weak” focusing. Here r is theradius of the beam and B is the magnetic field. Additionally the fieldindex needs to be maintained below 0.2, because at this value theperiodicity of radial oscillations and vertical oscillations of the beamcoincide in a ν_(r)=2 ν_(z) resonance. The betatron frequencies aredefined by ν_(r)=(1−n)^(1/2) and ν_(z)=n^(1/2). The ferromagnetic poleface is designed to shape the magnetic field generated by the coils sothat the field index n is maintained positive and less than 0.2 in thesmallest diameter consistent with a 250 MeV beam in the given magneticfield.

As the beam exits the extraction channel it is passed through a beamformation system 125 (FIG. 5) that can be programmably controlled tocreate a desired combination of scattering angle and range modulationfor the beam. Examples of beam forming systems useful for that purposeare described in U.S. patent application Ser. No. 10/949,734, titled “AProgrammable Particle Scatterer for Radiation Therapy Beam Formation”,filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088,filed Jul. 21, 2005, both of which are incorporated herein by referenceas if set forth in full. Beam formation system 125 may be used inconjunction with an inner gantry 601, which is described below, todirect a beam to the patient.

During operation, the plates absorb energy from the applied radiofrequency field as a result of conductive resistance along the surfacesof the plates. This energy appears as heat and is removed from theplates using water cooling lines 108 that release the heat in a heatexchanger 113 (FIG. 3).

Stray magnetic fields exiting from the cyclotron are limited by both thepillbox magnet yoke (which also serves as a shield) and a separatemagnetic shield 114. The separate magnetic shield includes of a layer117 of ferromagnetic material (e.g., steel or iron) that encloses thepillbox yoke, separated by a space 116. This configuration that includesa sandwich of a yoke, a space, and a shield achieves adequate shieldingfor a given leakage magnetic field at lower weight.

As mentioned, the gantry allows the synchrocyclotron to be rotated aboutthe horizontal rotational axis 532. The truss structure 516 has twogenerally parallel spans 580, 582. The synchrocyclotron is cradledbetween the spans about midway between the legs. The gantry is balancedfor rotation about the bearings using counterweights 122, 124 mounted onends of the legs opposite the truss.

The gantry is driven to rotate by an electric motor mounted to one ofthe gantry legs and connected to the bearing housings by drive gears andbelts or chains. The rotational position of the gantry is derived fromsignals provided by shaft angle encoders incorporated into the gantrydrive motors and the drive gears.

At the location at which the ion beam exits the cyclotron, the beamformation system 125 acts on the ion beam to give it properties suitablefor patient treatment. For example, the beam may be spread and its depthof penetration varied to provide uniform radiation across a given targetvolume. The beam formation system can include passive scatteringelements as well as active scanning elements.

All of the active systems of the synchrocyclotron (the current drivensuperconducting coils, the RF-driven plates, the vacuum pumps for thevacuum acceleration chamber and for the superconducting coil coolingchamber, the current driven ion source, the hydrogen gas source, and theRF plate coolers, for example), are controlled by appropriatesynchrocyclotron control electronics (not shown), which may include,e.g., a computer programmed with appropriate programs to effect control.

The control of the gantry, the patient support, the active beam shapingelements, and the synchrocyclotron to perform a therapy session isachieved by appropriate therapy control electronics (not shown).

As shown in FIGS. 1, 11, and 12, the gantry bearings are supported bythe walls of a cyclotron vault 524. The gantry enables the cyclotron tobe swung through a range 520 of 180 degrees (or more) includingpositions above, to the side of, and below the patient. The vault istall enough to clear the gantry at the top and bottom extremes of itsmotion. A maze 146 sided by walls 148, 150 provides an entry and exitroute for therapists and patients. Because at least one wall 152 isnever in line with the proton beam directly from the cyclotron, it canbe made relatively thin and still perform its shielding function. Theother three side walls 154, 156, 150/148 of the room, which may need tobe more heavily shielded, can be buried within an earthen hill (notshown). The required thickness of walls 154, 156, and 158 can bereduced, because the earth can itself provide some of the neededshielding.

Referring to FIGS. 12 and 13, for safety and aesthetic reasons, atherapy room 160 may be constructed within the vault. The therapy roomis cantilevered from walls 154, 156, 150 and the base 162 of thecontaining room into the space between the gantry legs in a manner thatclears the swinging gantry and also maximizes the extent of the floorspace 164 of the therapy room. Periodic servicing of the accelerator canbe accomplished in the space below the raised floor. When theaccelerator is rotated to the down position on the gantry, full accessto the accelerator is possible in a space separate from the treatmentarea. Power supplies, cooling equipment, vacuum pumps and other supportequipment can be located under the raised floor in this separate space.

Within the treatment room, the patient support 170 can be mounted in avariety of ways that permit the support to be raised and lowered and thepatient to be rotated and moved to a variety of positions andorientations.

In system 602 of FIG. 14, a beam-producing particle accelerator, in thiscase synchrocyclotron 604, is mounted on rotating gantry 605. Rotatinggantry 605 is of the type described herein, and can angularly rotatearound patient support 606. This feature enables synchrocyclotron 604 toprovide a particle beam directly to the patient from various angles. Forexample, as in FIG. 14, if synchrocyclotron 604 is above patient support606, the particle beam may be directed downwards toward the patient.Alternatively, if synchrocyclotron 604 is below patient support 606, theparticle beam may be directed upwards toward the patient. The particlebeam is applied directly to the patient in the sense that anintermediary beam routing mechanism is not required. A routingmechanism, in this context, is different from a shaping or sizingmechanism in that a shaping or sizing mechanism does not re-route thebeam, but rather sizes and/or shapes the beam while maintaining the samegeneral trajectory of the beam.

Referring also to FIG. 15, an inner gantry 601 may be included system602. In this example, inner gantry 601 is roughly C-shaped, as shown.Inner gantry 601 includes an applicator 610. Applicator 610 is mountedin a manner that permits applicator 610 to move along the surface 611 ofinner gantry 601 relative to patient support 606 (which is a differenttype of support than that depicted in FIG. 12). This enables theapplicator to be positioned anywhere within, e.g., a half-circle aroundthe patient, e.g., anywhere above, alongside, or below the patient 607.Applicator 610 may alter the particle beam provided by synchrocyclotron604. More specifically, as shown in FIG. 16, the particle beam 611provided by the beam shaping system of synchrocyclotron 604 may divergethe further the particle beam gets from the output of synchrocyclotron604. Applicator 610 may receive the particle beam from the output ofsynchrocyclotron 604 and alter characteristics of the particle beam. Forexample, applicator 610 may include an aperture and/or otherbeam-focusing mechanisms to substantially collimate the particle beam.As a result, the particle beam can be more precisely applied to a targetin the patient. For example, the particle beam can be sized and/orshaped to treat tumors of specific sizes and/or shapes. In this regard,applicator 610 is not limited to collimating the particle beam. Forexample, applicator 610 may reduce the size of the particle beam whilealso collimating the beam. The applicator may be a multi-leaf collimatorfor sizing and/or shaping the particle beam. Applicator 610 may alsosimply allow the particle beam to pass without alteration. Applicator610 may be computer controlled to affect the size and/or shape of thebeam, as desired.

Applicator 610 and synchrocyclotron 604 may move relative to patientsupport 606 (and thus the patient) and relative to one another. Forexample, movement of applicator 610 may substantially coincide withrotation of gantry 605, or one may follow the other, so that the outputof synchrocyclotron 604 aligns to the input of applicator 610. FIGS. 15and 17 illustrate movement of gantry 605 and movement of applicator 610along inner gantry 601. More specifically, FIG. 17 shows a case wheregantry 605 is rotated such that synchrocyclotron 604 is in a vault belowpatient support 606. In FIG. 17, synchrocyclotron 604 is below the floor612 of the treatment room, which floor may be made of concrete.Therefore, synchrocyclotron 604 is not visible in FIG. 17. In this case,applicator 610 is moved along inner gantry 601 so that applicator 610aligns to the output of synchrocyclotron 604. Because synchrocyclotron604 is not shown in FIG. 17, this alignment is not visible.Nevertheless, a particle beam output from synchrocyclotron 604 passesthrough cover 614 of inner gantry 601 and a corresponding hole in thefloor (not shown) and is thereafter is received by applicator 610.Applicator 610 performs any alteration on the particle beam, and passesthe particle beam to patient 607.

Gantry 605 (and thus synchrocyclotron 604) is rotatable relative to thepatient in the directions of arrow 615. Applicator 610 is movable alonginner gantry 601 in the directions of arrow 616. FIG. 15 shows thelocations of synchrocyclotron 604 and applicator 610 after the movementsdepicted by arrows 615 and 616, respectively. In FIG. 15, bothsynchrocyclotron 604 and applicator 610 are above patient support 606(and thus above patient 607). In this configuration, synchrocyclotron604 directs its particle beam downward, toward the patient. Applicator610 receives the particle beam, alters (e.g., collimates) the particlebeam, and passes the resulting particle beam to the patient.

Patient support 606 is movable relative to inner gantry 601, therebyenabling the patient to be moved such that a top part 621 of innergantry 601 is above the patient, and such that a bottom part 622 ofinner gantry 601 is below the patient. Movement of patient support 606,along with movement of gantry 605 and applicator 610, enables relativelyprecise targeting of tumors and/or other treatment areas on the patient.

FIG. 18 shows an example construction of inner gantry 601. In thisexample, inner gantry includes a structural weldment 617, a precisionlinear bearing rail 618 (e.g., a THK rail), cover 614, and applicator610 that includes an extension drive 619, and a theta drive 620. Innergantry 601 may include features in addition to those show, substitutionsfor the features that are shown, or both.

Structural weldment 617 may be constructed of any rigid material, suchas metal, plastic, or the like, which is capable of supporting theweight of applicator 610. In this example, structural weldment 617 issubstantially C-shaped (thereby defining the shape of inner gantry 601).It is noted, however, that structural weldment 617 may have othershapes. For example, it may be elongated or compressed. Basically,structural weldment may have any shape that enables relativelyunobstructed, continuous travel of applicator 610 between positions thatare above and below the patient.

Structural weldment 617 includes one or more bearing rails 618. Thenumber of rails that may be used depends upon the connection required toapplicator 610. Applicator 610 moves along bearing rail 618 between atop part 621 of structural weldment 617 and a bottom part 622 ofstructural weldment 617. The movement may be continuous or in discreteincrements and may be stopped at any point along bearing rail 618 inorder to obtain a desired position of applicator 610 relative to theposition of the patient.

Cover 614 covers what would otherwise be an open hole to the area belowfloor 612 (see FIG. 17). The hole and cover allow a particle beam topass from the synchrocyclotron to the applicator. Cover 614, however,prevents objects and/or other material from falling through that holeand possibly damaging sensitive equipment, such as the synchrocyclotron.Cover 614 may assist in, or control, movement of applicator 610 alongbearing rail 618. That is, cover 614 may roll along a path between thetop part 621 and the bottom part 622 of structural weldment 617. Cover614 may roll-up at its ends 624 and/or 625, as shown in FIG. 18.

Applicator 610 includes extension drive 619 and theta drive 620.Extension drive 619 moves aperture 625 towards, and away from, thepatent, e.g., along arrow 626. By virtue of this movement, extensiondrive may modify the projection of the aperture 625 on the patient. Forexample, the size of the aperture may be increased or decreased. Theshape of the aperture may be altered as well, e.g., between a circularshape, an oval shape, a polygonal shape, etc. Theta drive 620 movesapplicator 610 along rail 618 between top part 621 and bottom part 622of structural weldment 617. Cover 614 may travel along with applicator610.

All or part of extension drive 619 and theta drive 620 may becomputer-controlled. For example, extension drive 619 and/or theta drive620 may be controlled by the same hardware and/or software that is usedto control gantry 605.

System 602 is not limited to use with inner gantry 601. Any othermechanism may be used to provide an aperture to size and/or shape (e.g.,collimate) a particle beam provided by synchrocyclotron 604. Forexample, referring to FIG. 19, a robotic arm 626 may be used to positionan aperture 625 between synchrocyclotron 604 and the patient. Therobotic arm may move the aperture in three dimensions (e.g., XYZCartesian coordinates) relative to the patent. The robotic arm may becontrolled by the same hardware and/or software that is used to controlgantry 605. Additionally, the aperture itself may be controlled so thatits size and/or shape is modified. As described above, the size of theaperture may be increased or decreased. The shape of the aperture may bealtered as well, e.g., between a circular shape, an oval shape, apolygonal shape, etc.

An aperture, such as those described above, may be positioned and/orcontrolled manually. For example, a stand (not shown) may be used tohold the aperture. The aperture may be sized and/or shaped and placed onthe stand. Both the stand and the aperture may be positioned relative tothe patent and in line with the particle beam provided by thesynchrocyclotron. Any mechanism to hold the aperture may be used. Insome implementations, the aperture and/or device used to hold theaperture may be mounted to the synchrocyclotron itself.

The inner gantry is advantageous in that it reduces the precision withwhich the outer gantry must rotate. For example, the inner gantry allowssub-millimeter beam positioning. Because of the additional precisionadded by the inner gantry, the outer gantry need not providesub-millimeter precision, but rather its precision may be at, or greaterthan, a millimeter. The outer gantry also need not be as large as wouldotherwise be required in order to obtain high levels of precision.

Additional information concerning the design of the particle acceleratordescribed herein can be found in U.S. Provisional Application No.60/760,788, entitled “High-Field Superconducting Synchrocyclotron” andfiled Jan. 20, 2006; U.S. patent application Ser. No. 11/463,402,entitled “Magnet Structure For Particle Acceleration” and filed Aug. 9,2006; and U.S. Provisional Application No. 60/850,565, entitled“Cryogenic Vacuum Break Pneumatic Thermal Coupler” and filed Oct. 10,2006, all of which are incorporated herein by reference as if set forthin full.

Other implementations are within the scope of the following claims.Elements of different implementations, including features incorporatedherein by reference, may be combined to form implementations notspecifically described herein.

What is claimed is:
 1. A system comprising: a patient support to hold a patient; a synchrocyclotron to produce a proton or ion beam having an energy level sufficient to reach a target in the patient, the energy level being at least 150 MeV; a gantry on which the synchrocyclotron is mounted to move the synchrocyclotron through a range of positions around the patient on the patient support; and scanning elements that act on the proton or ion beam output from the synchrocyclotron, the scanning elements being between the patient and a location at which the proton or ion beam exits the synchrocyclotron.
 2. The system of claim 1, wherein the synchrocyclotron comprises ferromagnetic pole faces that define a space in which to accelerate particles to produce the proton or ion beam; and wherein the synchrocyclotron comprises an extraction channel to output the proton or ion beam from the synchrocyclotron.
 3. The system of claim 2, wherein the ferromagnetic pole faces comprises two ferromagnetic pole faces, each of the ferromagnetic pole faces being associated with a respective superconducting coil for carrying current to generate a magnetic field in the space to cause the particles in the space to travel in a spiral path that increases in radius as the particles move around the space prior to output to the extraction channel.
 4. The system of claim 3, wherein each of the ferromagnetic pole faces comprises a pole face configured to shape the magnetic field so that a field index is kept positive to maintain weak focusing within the space.
 5. The system of claim 1, wherein the synchrocyclotron comprises superconducting coils for carrying current to generate a magnetic field in a space to cause particles to travel in a spiral path; and wherein the synchrocyclotron comprises a helium-based cooling system to cool the superconducting coils to a superconducting temperature.
 6. The system of claim 1, wherein the synchrocyclotron comprises: superconducting coils to generate a magnetic field to support production of the proton or ion beam; a cold mass holding the superconducting coils; and straps to support the cold mass during movement of the gantry.
 7. The system of claim 6, wherein the synchrocyclotron comprises: an enclosure around the cold mass; and straps to support the cold mass within the enclosure during movement of the gantry, each of the straps comprising two links, a first of the two links connecting to the enclosure, and a second of the two links connecting to the cold mass.
 8. The system of claim 7, wherein the two links comprise a fiberglass link.
 9. The system of claim 1, wherein the synchrocyclotron is configured to produce a maximum magnetic field between 6 Tesla (T) and 20 T, and wherein the energy level is between 150 MeV and 300 MeV.
 10. A system comprising: a patient support to hold a patient; a synchrocyclotron to produce a proton or ion beam having an energy level sufficient to reach a target in the patient; and a gantry on which the synchrocyclotron is mounted to move the synchrocyclotron through a range of positions around the patient on the patient support; wherein the synchrocyclotron comprises: superconducting coils to generate a magnetic field; ferromagnetic pole faces to shape the magnetic field through a space in which particles are accelerated to form the proton or ion beam; a cryostat to maintain the superconducting coils at a superconducting temperature; and straps to support the cryostat, the straps being arranged based on gravitational force on the superconducting coils caused by rotation of the gantry.
 11. The system of claim 10, wherein the synchrocyclotron comprises an extraction channel to output the proton or ion beam from the synchrocyclotron.
 12. The system of claim 11, wherein the ferromagnetic pole faces comprises two ferromagnetic pole faces, each of the ferromagnetic pole faces being associated with a respective superconducting coil for carrying current to generate a magnetic field in the space to cause the particles in the space to travel in a spiral path that increases in radius as the particles move around the space prior to output to the extraction channel.
 13. The system of claim 12, wherein each of the ferromagnetic pole faces comprises a pole face configured to shape the magnetic field so that a field index is kept positive to maintain weak focusing within the space.
 14. The system of claim 10, wherein the synchrocyclotron comprises a helium-based cooling system to cool the superconducting coils to a superconducting temperature.
 15. The system of claim 10, further comprising: at least one scatterer in a path of the proton or ion beam between the synchrocyclotron and the patient.
 16. The system of claim 15, wherein each of the straps comprises two links, a first of the two links connecting to an enclosure around the cryostat, and a second of the two links connecting to the cryostat.
 17. The system of claim 16, wherein the two links comprise a fiberglass link.
 18. The system of claim 10, wherein the synchrocyclotron is configured to produce a maximum magnetic field between 6 Tesla (T) and 20 T, and wherein the energy level is between 150 MeV and 300 MeV.
 19. The system of claim 10, wherein the synchrocyclotron weighs less than 40 Tons and occupies a volume of less than 4.5 cubic meters.
 20. The system of claim 10, wherein the gantry comprises two arms, each of the two arms supporting a different side of the synchrocyclotron to rotate the synchrocyclotron through a range of positions around the patient on the patient support.
 21. The system of claim 1, wherein the synchrocyclotron comprises: superconducting coils to generate a magnetic field; ferromagnetic pole faces to shape the magnetic field through a space in which particles are accelerated to form the proton or ion beam; a cryostat to maintain the superconducting coils at a superconducting temperature; and straps to support the cryostat, the straps being arranged based on gravitational force on the superconducting coils caused by rotation of the gantry. 